NKCTF 2024 1z_F0r3ns1c5 Writeup

secret = 'pass ' + secret

for i in range(5, len(secret)-1):
    mosaic_img(canvas, W*i, 0, W*i+W, H//2)
    mosaic_img(canvas, W*i, H//2, W*i+W, H)

# 可改为如下形式
# 注释掉 secret 变量的字符串拼接，以及 range 范围从 0 开始
# secret = 'pass ' + secret

for i in range(len(secret)):
    mosaic_img(canvas, W*i, 0, W*i+W, H//2)
    mosaic_img(canvas, W*i, H//2, W*i+W, H)

H = 60
W = 30

from PIL import Image
import os

# 打开图片
img = Image.open("dict.png")
# img = Image.open("pass.png")

# 获取图片尺寸
width, height = img.size

# 定义切割尺寸
tile_width = 30
tile_height = 60

# 确保切割后的图片尺寸可以被整除
assert width % tile_width == 0 and height % tile_height == 0

# 创建 dict 文件夹
if not os.path.exists("dict"):
    os.makedirs("dict")
# if not os.path.exists("pass"):
#    os.makedirs("pass")

# 定义命名规则
char_set = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789"

# 切割图片并保存
for i in range(width // tile_width):
    for j in range(height // tile_height):
        tile = img.crop((i * tile_width, j * tile_height, (i + 1) * tile_width, (j + 1) * tile_height))
        index = i * (height // tile_height) + j
        filename = f"dict/{char_set[index]}"
        # filename = f"pass/{char_set[index]}"
        
 		# 如果文件名为大写字母，则添加 '-大写' 后缀
        if char_set[index].isupper():
            filename += "-大写"
        
        filename += ".png"
        
        tile.save(filename)

print("切割完成")

import os
import hashlib

def calculate_md5(filename):
    """计算文件的 MD5 值"""
    hasher = hashlib.md5()
    with open(filename, 'rb') as f:
        for chunk in iter(lambda: f.read(4096), b""):
            hasher.update(chunk)
    return hasher.hexdigest()

def get_file_md5(folder):
    """获取文件夹中所有文件的 MD5 值"""
    file_md5_dict = {}
    for file_name in os.listdir(folder):
        file_path = os.path.join(folder, file_name)
        if os.path.isfile(file_path):
            file_md5_dict[file_name] = calculate_md5(file_path)
    return file_md5_dict

# 读取 dict 文件夹中的所有文件的 MD5 值并存储到字典中
dict_folder = "dict"
dict_md5 = get_file_md5(dict_folder)

# 读取 pass 文件夹中的所有文件的 MD5 值并存储到字典中
pass_folder = "pass"
pass_md5 = get_file_md5(pass_folder)

# 找到 pass 文件夹中与 dict 文件夹中 MD5 值相同的文件名对应的 dict 中的 key
common_keys = [key for key, value in pass_md5.items() if value in dict_md5.values()]

print("Pass 文件夹中与 Dict 文件夹中 MD5 值相同的文件名:")

flag = ''
for key in common_keys:
    matching_keys = [k for k, v in dict_md5.items() if v == pass_md5[key]]
    for matching_key in matching_keys:
        flag += matching_key.split('.png')[0]

print(flag + '3')